Low frequency electromechanical oscillations have been major concerns for long-distance power transfers in many power systems. Insufficient damping of power systems can lead to oscillations with growing magnitudes, as was the case with the WECC blackout on Aug. 10, 1996. Such global oscillations, as well as local oscillations involving only one or several generators, can be disruptive to the safe operation of power systems.
Traditional techniques for detecting and controlling these low frequency electromechanical oscillations include modal analysis and Prony analysis of phasor measurements collected during the disturbances. These techniques, however, cannot provide early warnings for the disturbances and can be generally referred to as post-disturbance type techniques.
The ambient type techniques have proven to be more well-suited for early warning type on line damping estimation. The ambient measurements of power systems are collected when the system is in a normal operating condition using random load changes across the entire system for input. However, currently known ambient type techniques cannot compute the mode shape of the oscillatory modes nor give damping ratio estimation for any system condition significantly different from the current condition. In many cases, the growing or poorly damped oscillations are triggered by some radical system condition change, e.g., tripping the transmission lines, etc. The ambient type methods cannot handle such unexpected system changes. Accordingly, certain improvements for detecting and controlling low frequency electromechanical oscillations in power systems are needed.